Saboted-projectile, obturator



United States Patent 3,111,902 SABQTED-PROJECTILE, OBTURATOR Glenn Taylor, RED. 1, Box 168, Havre de Grace, Md. Filed Get. 8, 1962, Ser. No. 229,250 6 Claims. (Cl. 102-94) (Granted under Title 35, US. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment to me of any royalty thereon.

This invention relates to gun fired projectiles and has for its general object the improvement of such projectiles.

This invention is used in conjunction with saboted projectiles at all muzzle velocities, and more particularly, to a sabot adapted to hold the projectile either by friction or positive detent, thus providing for sealing of propellant gases and increasing the efiiciency of the sabot grip on the projectile.

Sub-calibering a projectile is an effective method, when used with a suitable light carrier or sabot, to greatly increase muzzle velocity. Such a sabot generally increases the area that presents itself to the propellant gas thrust. The decrease of mass of the total projectile package plus the increase in area acted upon by the gases allows a launcher to be used at its highest efiiciency. The majority of sabots to date use the sealing characteristics of the sabot proper to achieve seal or obturation of propellant gases. As the propellant gas pressure is increased, there is a high probability that with the sabot alone a gas leak will occur, particularly when other than 'a new or very good condition launch tube or gun is used. Also as the velocity is increased the wear due to friction causes the standard sabot to leak. If leakage or wear is sufficient the grip on the projectile may deteriorate the extent that failure occurs. This invention contemplates an obturator which will utilize the pressure in the launch tube or gun barrel to develop forces tending to seal the gases.

This invention further increases the efficiency of sabo-ts, either friction type or positive detent type, by compressing the sabot to the projectile by means of taper interference and the hydrostatic and viscoelastic force properties of nonsrnetallic plastic materials.

According to this invention, a projectile is made of substantially less diameter than the bore of the gun from which it is to be fired, and it is surrounded by an annular collar, commonly known as a sabot, to increase the area on which the propellant gases act in order to increase the total propelling force. In addition, an obturator is provided to ensure a gastight seal of the propellant gases on the surfaces of the projectile-sabot combination.

It is the object of this invention to provide a simple and economical obturator for saboted projectiles.

It is another object of this invention to provide a method of increasing the elliciency of sabots of all types.

It is a further object of this invention to provide an obturator that utilizes. propellant gas pressure to deform hydrostatically the non-metallic material, thus increasing the efiiciency of obturation.

Yet another object of this invention is to provide an obturator which is easy to manufacture, simple to install on the saboted projectile, effective in producing higher projectile velocities.

Still a further object of this invention is to allow the use of light materials such as plastics and other deformable non-rnetals to decrease the total mass of gun fired missiles, and thus increase the acceleration imparted to a projectile by the propellant.

The novel features that are considered characteristic of this invention are set forth with particularity in the appended claims. The invention itself, however, both as to FIGURE 3 is a view of a projectile-sabot combination 1 with a cross-sectioned obturator in place which shows a weak flare skirt on the rear face; and

FIGURE 4 is a perspective View of the second embodiment of the obturator with a flare skirt.

In FIG. 1, there is shown a typical basic sabot-projectile combination. Sabot 1 may be anchored to the projectile 2 by means. of positive detent or friction. The obturator 3 is shown aft of the sabot l in intirnate contact with the sabot and projectile. The projectile 2 is normally of uniform cross-section and has its axis coincident with the bore of gun 4. Although obturator 3 herein disclosed is especially adaptable for use with this type of conical sabot, it is not limited to use with this type and may be used with any angle sabot configuration as necessary to promote efficiency of operation.

As shown in FIG. 2, the obturator is split longitudinally as indicated at 5 with precise matching surfaces to provide release or separation from the projectile-sabot combination when emerging from the launcher muzzle. Since the sabot itself normally contains such splits also, the obturator and sabot are thus so designed that on leaving the gun muzzle they break up and disintegrate under the action of rnuzzlle blast, air lift or centrifugal force due to the spin of the combination produced by the rifting usually found in a gun bore. This allows for the parts to fall apart, and leave the projectile itself to continue on its flight towards the target.

It is shown in FIGS. 1 and 2 that the obturator 3 includes an opening extending longitudinally along its axis and around the projectile-sabot combination. The obturator is not limited to use with through type combinations however, and may be adapted to flat base projectiles by omitting the axial opening.

Normally the exterior cylindrical surface of obturator 3 is adapted to the bore and is machined [for either a close or slightly over-size fit depending on the performance level of the launch tube or gun bore 4. Generally speaking, the higher the anticipated propellant gas pressure, the greater the interference with the gun bore should be to prevent leakage of propellant gases when the gun or launcher is fired. This contemplated design also increases the here or interior ballistic stability of the projectile by adding length to the projectile-sabot combination Where it is in contact with the launch tube bore.

Upon firing of the launch tube or gun, the propellant gas pressure is applied to the rear 6 of obturator 3 cansing deformation of the non-metallic plastic material due to the resulting hydrostatic force or viscoelastic phenomena. Obturator 3 engages intimately with the launch tube or gun bore or barrel following the contour of the surface 7. The obturator also becomes intimately associated with sabot l, sealing any flaws, defects, cuts or cracks, at the same time the same force is exerted against the projectile body at the surface 3 of that body, thus providing a seal at this location. The amount of the non-metallic obturator material is a function of maximum propellant gas pressure and interior ballistic stability desired and total package weight or mass considerations. The hydrostatic [force and deformation of the non-metallic plastic material of the obturator seals all surfaces of the obturator to the bore of gun 4, sabot l and projectile 2, thus forming a very efficient seal.

Examples of plastic materials suitable for this. inven- 6! tion, not intended as a limitation, are linear polyethylene for low performance levels, ethylcellulose for intermediate performance levels and polycarbonate for high performance levels over 8,000 ft./ sec.

FIGS. 3 and 4 show a low level obturator. For low performance levels where propellant gas pressure is either of a low value or long duration of time to maximum pressure, the additional feature of a flare skirt 9 is added as low level obturation. The mechanical-dynamic action of this obturator is the same as previously described. However, due to its rather thin or fragile nature, the cuplike flare skirt deforms at much lower performance levels than the type shown in FIGS. 1 and 2. An additional feature of the flare skirt is in aiding separation from the projectile-sabot combination. It is a well known fact that for a short period of time after leaving the launch tube the projectile i in reality flying backwards with respect to the flow of propellant gases. The flare skirt acts as a partial container and a resulting thrust transverse to the axis of the projectile and away from the projectile occurs. This thrust or force moves the obturator forward and away, transversely, and the obturator separates at the previously mentioned splits 5.

In summary this invention is concerned with a nonmetallic obturator exhibiting hydrostatic-viscoelastic properties which is adapted to a projectile-sabot combination to be propelled along the axis of a launch tube or gun bore wherein the obturator has projectile-sabot mating surfaces as necessary to produce intimate contact. Since the obturator has a rear portion or face exposed to the propellant as forces, the pressure caused by these gases and the projectile-sabot mating surfaces force the obturator to grip the projectile and sabot causing constricting forces in addition to those normally obtained in projectile-sabot combinations.

Although specific embodiments of this invention have been illustrated and described, it will be understood that this is but illustrative and that various modifications may be made therein without departing from the scope and spirit of the invention.

What is claimed is:

l. Ammunition of the type described comprising an elongated projectile of substantially uniform cross-section, the longitudinal axis of said projectile being aligned with the axis of a gun bore through which the projectile is adapted to be propelled; a sabot having a cylindrical front portion adapted to slidably engage the walls of the bore, said sabot having a eonstrieta'ole rear portion engaged around the projectile, the rear portion including a tapered portion extending from the cylindrical front portion to the rear end of said rear portion with said rear end being of a diameter smaller than that of the cylindrical front portion; and a non-metallic obturator exhibiting hydrostaticwiscoelastic properties having a cylindrical exterior portion adapted to slidably engage the walls of the bore, said obturator having a tapered front portion engaged around the rear portion of the sabot, a central portion engaged around the projectile, and a rear portion exposed to propellant gas forces, wherein the pressure caused by the propellant gases forces the obturator to grip the projectile and sabot at the engagement surfaces between the obturator and each of said sabot and projectile causing constricting forces in addition to those normally present projectile-sabot combinations and thereby preventing leakage of the propellant gases.

2. The ammunition described in claim 1 wherein said obturator is composed of ethylcellulose.

3. The ammunition described in claim 1 wherein said obturator is composed of polycarbonate.

4. Ammunition as described in claim 1 wherein the ront end of the sabot and the obturator are of a flaring funnel-shaped configuration and are made up of sections thus providing for air to strip the sabot and obturator from the projectile when the ammunition passes out from the gun barrel.

5. The ammunition described in claim 1 where-in the rear portion of said obturator includes a cup-like flare skirt at its outer edge which deforms at low propellant gas pressures.

6. The ammunition described in claim 4 wherein said obturator is composed of polyethylene.

References Cited in the file of this patent UNITED STATES PATENTS 35,521 James June 10, 1862 37,979 Roberts Mar. 24, 1863 178,595 Butler June 13, 1876 195,040 Owen Sept. 11, 1877 2,939,395 Barr June 7, 1960 3,005,408 Prosen et a1. Oct. 24, 1961 

1. AMMUNITION OF THE TYPE DESCRIBED COMPRISING AN ELONGATED PROJECTILE OF SUBSTANTIALLY UNIFORM CROSS-SECTION, THE LONGITUDINAL AXIS OF SAID PROJECTILE BEING ALIGNED WITH THE AXIS OF A GUN BORE THROUGH WHICH THE PROJECTILE IS ADAPTED TO BE PROPELLED; A SABOT HAVING A CYLINDRICAL FRONT PORTION ADAPTED TO SLIDABLY ENGAGE THE WALLS OF THE BORE, SAID SABOT HAVING A CONSTRICTABLE REAR PORTION ENGAGED AROUND THE PROJECTILE, THE REAR PORTION INCLUDING A TAPERED PORTION EXTENDING FROM THE CYLINDRICAL FRONT PORTION TO THE REAR END OF SAID REAR PORTION WITH SAID REAR END BEING OF A DIAMETER SMALLER THAN THAT OF THE CYLINDRICAL FRONT PORTION; AND A NON-METALLIC OBTURATOR EXHIBITING HYDROSTATIC-VISCOELASTIC PROPERTIES HAVING A CYLINDRICAL EXTERIOR PORTION ADAPTED TO SLIDABLY ENGAGE THE WALLS OF THE BORE, SAID OBTURATOR HAVING A TAPERED FRONT PORTION ENGAGED AROUND THE REAR PORTION OF THE SABOT, A CENTRAL PORTION ENGAGED AROUND THE PROJECTILE, AND A REAR PORTION EXPOSED TO PROPELLANT GAS FORCES, WHEREIN THE PRESSURE CAUSED BY THE PROPELLANT GASES FORCES THE OBTURATOR TO GRIP THE PROJECTILE AND SABOT AT THE ENGAGEMENT SURFACES BETWEEN THE OBTURATOR AND EACH OF SAID SABOT AND PROJECTILE CAUSING CONSTRICTING FORCES IN ADDITION TO THOSE NORMALLY PRESENT IN PROJECTILE-SABOT COMBINATIONS AND THEREBY PREVENTING LEAKAGE OF THE PROPELLANT GASES. 